Method for graftless spinal fusion

ABSTRACT

A graftless spinal implant for mechanically attaching two adjacent vertebrae includes a body having first and second opposite surfaces. The first and second surfaces include at least one protruding member for securing the body to adjacent vertebrae, wherein the exterior surfaces of the body and the first and second protruding members include a bioactive coating. The bioactive coating can be selected from coatings such as for example, hydroxyapatite. The exterior bioactive coating facilitates the ongrowth/ingrowth of vertebral bone between the implantable spinal fusion device and adjacent vertebrae. Advantageously, spinal fusion may be achieved without the use of a bone graft and/or bone growth agents.

[0001] This application is a divisional application of U.S. patentapplication Ser. No. 09/976,685, entitled “Graftless Spinal FusionDevice,” filed Oct. 11, 2001, which claims priority from the provisionalapplication designated serial No. 60/239,368, filed Oct. 11, 2000entitled “Spinal Fusion Device.” Each of these applications is herebyincorporated by reference herein.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to spinal implants, and inparticular to a graftless spinal implant that employs a bioactivecoating such as hydroxyapatite to promote fixation of the implant toadjacent bony surfaces.

[0003] U.S. Pat. No. 6,241,769 entitled “Implant for Spinal Fusion” andU.S. Pat. No. 6,096,080 entitled “Apparatus for Spinal Fusion UsingImplanted Devices” disclose spinal replacement devices. Both patentsdiscuss in detail the problems associated with the prior art devices.

[0004] The devices disclosed in U.S. Pat. Nos. 6,241,769 and 6,096,080,each hereby incorporated by reference, utilize a central graft space forpromoting the long-term fixation onto adjacent bony surfaces. The devicecan be fabricated from human bone allograft material of bone substitutematerial such as coral or calcium phosphate. A problem with the devicesdisclosed in these patents is that they require a bone graft, and thefailure rate of these types of devices is fairly high. In addition,there is an unacceptably high rate of morbidity (e.g., 30%).

[0005] Therefore, there is a need for a spinal implant device that doesnot utilize a bone graft in an attempt to facilitate fixation of theimplant device to adjacent vertebral bony surfaces, and therebystabilize the spinal motion segment.

SUMMARY OF THE INVENTION

[0006] Briefly, according to the present invention, an implantablespinal fusion device includes an exterior bioactive coating.

[0007] In one embodiment, a graftless spinal implant for mechanicallyattaching two adjacent vertebrae includes a body having first and secondopposite surfaces. The first and second surfaces include at least oneprotruding member for securing the body to adjacent vertebrae, whereinthe exterior surfaces of the body and the first and second protrudingmembers include a bioactive coating.

[0008] The bioactive coating can be selected from coatings such as forexample, hydroxyapatite, bioglass, biocomposites, hydroxypatitetricalcium phosphate, bone morphogenic protein, or other bone producingproteins.

[0009] The exterior bioactive coating facilitates the ongrowth/ingrowthof vertebral bone between the implantable spinal fusion device andadjacent vertebrae. Advantageously, this allows the device to avoid theuse of a bone graft and/or bone growth agents.

[0010] These and other objects, features and advantages of the presentinvention will become apparent in light of the following detaileddescription of preferred embodiments thereof, as illustrated in theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 illustrates a perspective view of a first embodiment of agraftless spinal implant;

[0012]FIG. 2 illustrates a front view of the graftless spinal implantoperably implanted within a spine;

[0013]FIG. 3 illustrates a side view of the graftless spinal implantshown in FIG. 2.

[0014]FIG. 4 illustrates a perspective view of a second embodiment of agraftless spinal implant;

[0015]FIGS. 5-6 illustrate additional perspective views of the graftlessspinal implant illustrated in FIG. 4; and

[0016]FIG. 7 illustrates yet another embodiment of a graftless spinalimplant.

DETAILED DESCRIPTION OF THE INVENTION

[0017]FIG. 1 illustrates a graftless spinal anterior fusion device 10.The device 10 includes a main body 12, which in this embodiment issubstantially rectangularly shaped. However, one of ordinary skill willrecognize that the main body 12 may be configured in shapes other thanrectangular. The main body 12 also includes first and second oppositesurfaces 14, 16 respectively. In this embodiment the first and secondsurfaces 14, 16 are substantially parallel, and include protrudingmembers 18-21. The main body and protruding members are preferably a onepiece (i.e., unitary) structure. The device 10 may also have a gentlecurve/taper.

[0018]FIG. 2 is a simplified illustration of the graftless spinalanterior fusion device 10 operably implanted within a spine 24. Thespine includes vertebrae 26, 28 and natural disks 30, 32. The spine 24also includes a diseased/damaged disk 34 that has been partially removedand replaced with the graftless spinal anterior fusion device 10 of thepresent invention. In preparation for the surgical insertion of thegraftless spinal anterior fusion device 10, keyways 36-39 sized tosecurely accept an associated protruding member (e.g., 18-21) are formedin each of the vertebrae 26, 28 located adjacent to the damaged/diseaseddisk.

[0019]FIG. 3 illustrates a side view of the graftless spinal implant 10shown in FIG. 2. Notably, extension and rotational forces areneutralized by the protruding members.

[0020] According to an aspect of the present invention, the device 10 iscoated with a bioactive coating, such as for example, hydroxyapatite,bioglass, biocomposites, hydroxypatite tricalcium phosphate, bonemorphogenic protein, or other bone producing proteins. Significantly,the bioactive coating facilitates ongrowth/ingrowth of vertebral bone.

[0021]FIG. 4 illustrates a perspective view of a second embodiment of agraftless spinal implant 70. This embodiment also includes asubstantially rectangular main body 72, and at least one protrusion(e.g., 74-77) extending from each of first and second opposite surfaces80, 82. Notably, the protrusions 74-77 are substantially cylindricallyshaped. Of course, keyways (not shown) formed in adjacent vertebrae areshaped to accept the protrusions 74-77. In addition, the exteriorsurfaces of this graftless spinal implant 70 are textured/roughed andinclude a plurality of depressions 79, which increases the surface areaof the implant. That is, the exterior surfaces of the graftless spinalimplant 70 preferably include a plurality of shallow depressions 79 tofacilitate fusion of the implant and adjacent bone. The textured surfacemay include beads, arc deposits, and/or synthetic foams. The exteriorsurfaces of the implant 70 are coated with a bioactive coating, such asfor example, hydroxyapatite. This coating facilitates ongrowth/ingrowthof vertebral bone. The exterior surfaces of the device illustrated inFIGS. 1-4 in a preferred embodiment are preferably similarly roughenedand include a plurality of depressions.

[0022] In an alternative embodiment, the implant 70 may include anopening 84 into which bone growth agents may be placed, as disclosed inthe above identified U.S. patents incorporated herein by reference. Theresultant device may no longer be considered a pure graftless device dueto the inclusion of bone graft materials that are placed into theopening. Significantly, this device combines advantages of the graftlessdevice discussed above, and features of the prior art graft techniques.The opening 84 may extend through the main body 72 (i.e., it is athrough hole), or it may extend only partially through the main body 72.The surfaces that define the opening preferably may also betextured/roughened and include shallow depressions/holes.

[0023]FIGS. 5 and 6 are additional perspective views of the graftlessspinal implant 70.

[0024]FIG. 7 illustrates a perspective view of yet another embodiment ofa graftless spinal implant 100. This spinal implant is substantially thesame as the implant illustrated in FIGS. 4-6, with the exception thatthis embodiment includes tapered edges 102 on at least one side of thedevice. The tapered edges 102 facilitate inserting the implant into thekeyways (not shown) cut into the vertebrae. In this embodiment theimplant 100 is also coated with a bioactive coating, such as forexample, hydroxyapatite.

[0025] The implant itself may include a variety of presently acceptablebiocompatible materials such as Titanium, Polyphenolsulfone,Polyaryletherketone (PEEK), Polysulfone, Acetal (Delrin), UHMWPolyethylene, and composites of these materials involving high strengthcarbon fibers or REM glass filaments to add tensile and shear strength.The implant may also be fabricated from human bone allograft material,autograft material, or bone substitute material, such as coral orcalcium phosphate. The body of the implant may optionally have a modesttaper.

[0026] Although the embodiments illustrated above employ protrudingmembers that are substantially dovetail shaped or cylindrical/horse-shoeshaped, it is contemplated that essentially any shaped protruding membermay be used with the bioactive coated implant of the present invention.

[0027] Although the present invention has been shown and described withrespect to several preferred embodiments thereof, various changes,omissions and additions to the form and detail thereof, may be madetherein, without departing from the spirit and scope of the invention.

What is claimed is: 1) A method for fusing a first vertebra to a secondadjacent vertebra, the method comprising: a) providing an implant, theimplant comprising a body having first and second opposite surfaces,wherein each of the surfaces includes at least one protruding member forsecuring the body to an adjacent vertebra and wherein the implant hassufficient tensile and sheer strength to permit fusion of the vertebraeand each of the surfaces and protruding members includes a bioactivecoating; b) forming at least one keyway in the first vertebracorresponding to each of the at least one protruding members on thefirst surface and at least one keyway in the second vertebracorresponding to each of the at least one protruding members on thesecond surface; and c) inserting the implant between the first vertebraeand the second vertebra in a manner so that each protruding memberslides into the corresponding keyway, such that fusion of the vertebraeis achieved without a bone graft. 2) A method according to claim 1,wherein at least one of the opposite surfaces of the implant includes aplurality of protruding members. 3) A method according to claim 1wherein at least one protruding member of the implant includes a pair ofbulges, the bulges on opposite sides of a plane perpendicular to thesurface, the plane passing through a point on the at least oneprotruding member that is at a maximum distance from the surface, thebulges such that a projection of each bulge on the corresponding surfaceis larger than the projection on the corresponding surface of anyportion of the protruding member that is closer to the surface thaneither bulge, so that the at least one protruding member is shaped toprovide keyed engagement with a vertebra that has been suitably preparedto receive the at least one member. 4) A method according to claim 1,wherein the at least one protruding member of the implant has a profileincluding a generally arcuate portion that encompasses more than onehundred and eighty degrees. 5) A method according to claim 1, whereinthe at least one protruding member of the surface includes exactly twomembers.